In #26672 we blocked use of Ruby keywords as identifiers for view
locals but inadvertently broke the use of instance variable names
as identifiers. Whilst not explicitly documented this behavior has
been around for a long time and there's no need to break it now.
Fixes#27480.
this lets you pass ruby keywords to templates:
<%= render 'example', class: "cool" %>
<%= render 'example', "spaces are" => "a-ok" %>
<%= render 'example', Foo: "bar" %>
Previously you'd see confusing syntax errors like this:
SyntaxError (.../_example.html.erb:1: syntax error, unexpected '='
Now you can reference invalid identifiers through local_assigns.
If you try to use an invalid keyword (e.g. class) in your template, you
get a syntax error on the line where you use it.
